add describe masks (count pixel occurrences)

[johnnv1]

No description provided.

[codecov]

Codecov Report

Merging #50 (00e11ac) into main (60aec8b) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main       #50   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           46        46           
  Lines         3376      3441   +65     
  Branches       374       386   +12     
=========================================
+ Hits          3376      3441   +65     

Impacted Files	Coverage Δ
CCAgT_utils/describe.py	100.00% <100.00%> (ø)
tests/describe_test.py	100.00% <100.00%> (ø)

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